1. Field of the Invention
The present invention relates to a vehicle spring apparatus. The present invention also relates to a vehicle height adjusting system using such a vehicle spring apparatus.
2. Technical Background
In vehicles having a relatively large load-carrying capacity, e.g. vans or station wagons, the vehicle height may vary to a considerable extent with a change in carrying load depending on the fact that occupants get on and off the vehicle, or goods or baggage is loaded onto or unloaded from the vehicle. This affects the body motion control and the steering system. Therefore there has been a demand for a suspension apparatus capable of automatically maintaining ride height irrespective of variations in the carrying load.
There has heretofore been proposed damper suspension means for vehicles, for example, in U.S. Pat. No. 4,273,358. In this prior art hydraulic damper, an oil tank and a reservoir have a high-pressure gas sealed therein. A pump device supplies a hydraulic fluid from the oil tank into a working chamber to provide response pressure to the extension and the contraction of a piston rod. At least one diaphragm is provided to separate the different media in the working chamber. This prior art system is one of many examples of systems using controlled hydro pneumatic units with a pressure supply from a hydraulic pump.
The hydraulic supply calls for hydraulic linings and hydraulic pumps and is complex and generally makes the manufacturing process of a vehicle complicated, costly and time-consuming.
An alternative to the above outlined system is a self-pumping hydraulic damper. However, this prior art self-pumping hydraulic damper suffers from some issues. After a vehicle equipped with the self-pumping hydraulic damper has run with no baggage loaded thereon, the pressure of the hydraulic fluid in the cylinder has been adjusted to a low level according to the small carrying load. If the vehicle in under these conditions is loaded with baggage, the vehicle height is lowered by an amount corresponding to an increase in the carrying load. As the vehicle loaded with the baggage runs, the pump device operates to supply the pressure fluid from the oil tank into the working chamber, causing the vehicle height to rise gradually. In this way, the vehicle height is adjusted to a predetermined level. In this case, when starting running when pumping has not yet been sufficiently effected, the vehicle runs in a state where the vehicle height is still low.
Accordingly, the road clearance is insufficient, and the underside of the vehicle is likely to touch the ground. Therefore, when the carrying load is heavy or when the vehicle passes an uneven spot on the road, the underside of the vehicle may touch the ground unfavorably.
U.S. Pat. No. 6,092,816 describes a system with a high pressure accumulator tank connected to a working chamber via a switching valve. The pressure of the system may also be relieved. Accordingly, the vehicle height can be adjusted to a level within the standard vehicle height range even immediately after the vehicle in unloaded condition has been loaded with baggage, for example.
It is of course important to improve the driving safety, maintaining the body motion control and the tire-road contact also in severe maneuvers and other extreme situations outside the standard vehicle range, without causing damage to the spring and damper system of the vehicle. At the same time it is important to provide a system that is robust, simple and easy to manufacture and yet not overly costly.
The object of the present invention is to provide a spring apparatus that overcomes the above issues, and makes it possible to provide an actively controllable vehicle spring apparatus.
A further object of the present invention is to provide a vehicle spring apparatus integrated in one unit.
It is still a further object to provide a spring apparatus that achieves these and other objects but are yet inexpensive and especially simple to manufacture and install in a vehicle.
These and other objects are achieved by a spring apparatus according to claim 1. Preferred embodiments of the invention is defined in given by the dependent claims. A further object is to provide an accurate and reliable vehicle height adjusting system, which system is further described in claim 9.
According to the invention there is provided a vehicle spring apparatus comprising, a housing having fluid sealed therein, the housing comprising, a cylinder with a slidably fitted piston, a piston rod connected at one end thereof to the piston, the piston rod extending at the other end thereof to outside of the cylinder, characterized in that, the cylinder is connected via a passage and a first valve to a first accumulator chamber comprising a springing medium, the cylinder is connected via a passage and a second valve to a second accumulator chamber comprising a springing medium, and the accumulator chambers also being connected with each other via at least one controllable pump.
This arrangement makes it possible to provide an actively controllable springing of a vehicle spring apparatus, which apparatus is simple to manufacture and install in a vehicle. The response to the strokes of the piston rod caused by vibrations of the vehicle during running will cause pressure changes in the apparatus. Both the accumulators are fitted with a springing medium. When the piston rod is in motion, the apparatus is preferably arranged so that one valve only allows fluid into its accumulator causing an increase of the pressure in the accumulator and the other valve only permits fluid to exit from its accumulator, which result in a flow into one of the accumulators and out of the other accumulator depending on the strokes of the piston rod. The pressure thus increases in one of the accumulators and decreases in the other accumulator of the spring apparatus. The higher pressure in one of the two accumulators, the higher force acting from the spring apparatus is achieved. A controllable pump controls the pressure difference between the two accumulators so that a least a necessary and even desired pressure range is adaptable during operation.
In an embodiment of the inventive vehicle spring apparatus, there is provided a passage for transporting the fluid from one side to one other side of the piston. This makes it possible to connect a damper to the passage in accordance with a second embodiment of the invention. Thus a springing and damping apparatus is provided that may be integrated in one unit. By virtue of the above-described arrangement, a robust vehicle spring apparatus can be obtained.
In a preferred embodiment of the invention the controllable pump is electrically controlled. Thus, the apparatus can be integrated into one electrically fed unit. This arrangement makes it possible to provide a spring and damper apparatus that is not dependent on external hydraulic supply. Hydraulic prior art systems are sometimes complex and difficult to install in a vehicle. By providing the possibility of an integrated springing apparatus the manufacturing process is facilitated.
The vehicle spring apparatus is in a preferred embodiment adapted for connection between sprung and unsprung parts of a vehicle. The simple structure which constitutes a preferred embodiment of the present vehicle spring apparatus invention makes it easy to connect sprung and unsprung parts, and preferably the body and the wheel-suspension of a vehicle are connected by means of the spring apparatus.
In a further preferred embodiment of the invention the first valve is a unidirectional valve only permitting flow in the direction from the cylinder towards the first accumulator and the second valve is a unidirectional valve only permitting flow in the direction from the second accumulator and towards the cylinder.
It is a further advantage of the present invention that by using simple unidirectional valves the need for steering and switching valves to achieve desired pressure levels in the apparatus is kept at a minimum.
In an embodiment of the present invention the vehicle spring apparatus comprises a connection to a control unit for controlling the apparatus actively. This control unit provides a further advantage of the inventive spring apparatus in making the active control of the unit more precise.
The invention also relates to a vehicle height adjusting system comprising the spring apparatus and, vehicle height detectors for detecting the vehicle height, a control unit, the vehicle spring apparatus being provided between sprung and unsprung parts of the vehicle, wherein the pump fitted between the accumulator chambers may be fed with power for transferring fluid from the second accumulator chamber to the first accumulator chamber in order to increase the distance between sprung and unsprung parts of the vehicle, whereas when the distance between sprung and unsprung parts of the vehicle is to be reduced a fluid transfer from the first accumulator chamber to the second accumulator chamber is performed. This height adjusting system provides a robust, simple and safe system for keeping at least a necessary vehicle height range during operation.
In a further embodiment of the invention a vehicle is provided with at least one vehicle spring apparatus. In an alternative further embodiment of the invention a vehicle is provided with one spring apparatus between the body and wheel-suspension in each of the four corners of the vehicle. In a preferred embodiment of the invention there is provided a vehicle comprising a height adjusting system. The height adjusting system according to the invention comprises a vehicle spring apparatus. This arrangement makes it possible to provide a vehicle with more accurate springing and damping in relation to the prevailing operating conditions.